SAN FRANCISCO — Reggie Jackson watched Pablo Sandoval join his exclusive club by hitting two of his three Game 1 homers off Justin Verlander and came away impressed.

“I saw it and that was awesome. He may have hit two of the three against the best pitcher in baseball,’’ Jackson told The Post before the Giants’ grabbed a 2-0 World Series lead with a 2-0 victory over the Tigers Thursday night. “I haven’t seen Clayton Kershaw, the lefty from the Dodgers and the knuckleballer from the Mets [R.A. Dickey], but this guy [Verlander] is the most dominant in the game. You hit two homers off him in a World Series game you are doing something. The first one was a 95-mph out of the strike zone. You have to tip your cap to that.’’

Jackson was more than happy to make room for a fourth chair at the table that sits the men who have hit three homers in a World Series game. Sandoval joins Babe Ruth (twice), Albert Pujols and Jackson, who hit his three homers in Game 6 of the 1977 World Series in the Yankees’ series-clinching win over the Dodgers.

Sandoval did it one year after Pujols, then with the Cardinals, swatted three homers against the Rangers in Game 3 last year.

“He is fun to watch, when he gets done swinging his shirt tail comes out of his pants. It’s a fun thing to see, a lovable chubby guy. You can’t help but like him,’’ Jackson said of the switch-hitting slugger who is listed at 5-foot-11 and 240 pounds, though that weight total appears to be generous. “He is a big kid. If he goes home in a Mercedes, it’s probably a six-door car.’’

Jackson said he has met Sandoval once when he threw out a ceremonial first pitch at AT&T Park early in the 2011 season. Yesterday, Jackson was looking to get in touch with Sandoval.

“I will try and get a hold of him, reach out to him and say congratulations,’’ Jackson said.

Before last night’s Game 2 when the Giants were looking to grab a 2-0 lead in the best-of-seven affair, Sandoval said he hadn’t heard from Jackson or Pujols but believed the Angels slugger was in his corner.

“Pretty much Albert is happy, Pujols is happy for all the things happening right now for me,’’ said Sandoval, who received a tweet from Venezuela president Yugo Chavez Wednesday night.

When Sandoval launched the third homer in the fifth inning off Al Alburquerque, Jackson started thinking about someone hitting three homers in a World Series game two straight years after Ruth and Jackson were the only members.

“I thought about that again this morning, that it took 34, 35 years for someone to do it and then it happens twice in a row,’’ Jackson said. “But Sandoval has been swinging the bat as well as anybody in the game the last 10 days or so.’’

Before facing Tigers right-hander Doug Fister in Game 2, Sandoval was batting .370 (20-for-54) with six homers and 13 RBIs in 13 postseason games with an OPS of 1.164. Sandoval had 12 homers during the regular season.

Jackson has a home in the Bay Area but was in Southern California when Sandoval turned a three-man fraternity into four Wednesday night. And with a possible six games remaining, Sandoval has a chance to become the first ever to hit four in a game.